24 BA CTEEIOL OGY. 



into a fine tube, bend it down along the side of the 

 flask, and then bend it up again a few centimetres from 

 its extremity, and leave the mouth open. The infusion 

 was then to be boiled in the flask thus prepared and the 

 mouth of the tube left open. The organisms which 

 now fell into the open end of the tube were arrested by 

 the drop of water of condensation which collected at its 

 lowest angle, and none could enter the flask. 



While, from our modern standpoint, the results of 

 these investigations seem to be of a most convincing 

 nature, yet there were many at the time who required 

 additional proof that "spontaneous generation" was 

 not the explanation for the mysterious appearance 

 of these minute living creatures. The majority, if 

 not all, of such doubts were subsequently dissipated 

 through the well-known investigations of Tyndall upon 

 the floating matters of the air. In these studies he 

 demonstrated by numerous ingenious and instructive 

 experiments that the presence of living organisms in 

 decomposing fluids was always to be explained either 

 by the pre-existence of similar living forms in the infu- 

 sion or upon the walls of the vessel containing it, or 

 by the infusion having been exposed to air which had 

 not been deprived of its viable organisms. 



Throughout all the work bearing upon this subject^ 

 from the time of Spallanzani to that of Tyndall, certain 

 irregularities were constantly appearing. It was found 

 that particular substances required to be heated for a 

 much longer time than was needed to render other 

 substances free from living organisms, and even after 

 heating under the most careful precautions decomposi- 

 tion would occasionally occur. 



In 1762 Bonnet, w r ho was deeply interested in this 



